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Abstract

We have demonstrated the operation of a new type of heterogeneous photonic crystal laser, a five-lattice-constant large photonic bandedge laser assisted by a photonic bandgap, in a triangular lattice at room temperature. When the air hole radius of the surrounding photonic crystal (PC) is slightly smaller than that of the bandedge mode region, most in-plane losses of the first K point bandedge mode in the central region are suppressed and the quality factor of the mode is greatly enhanced to 50000. We identified the photonic bandgap-bandedge (PBG-BE) lasing modes through the spectral position, near-field pattern, and the state of polarization, which correspond well with the results of the three-dimensional (3D) finite-difference time-domain (FDTD) method computation. The two-dimensional (2D) feedback mechanism of the first K bandedge was verified through the Fourier analysis. Low threshold incident peak pump power of ~ 0.24 mW is achieved owing to the low optical loss of the PBG-BE mode.

Figures (4)

(a) Top-view scanning electron microscope (SEM) image of a fabricated PBG-BE laser. The lattice constant is 390 nm. The air hole radius of the central hexagon region (I) with five holes along the ΓK direction, and that of surrounding region (II) are 137 nm (0.35a) and 117 nm (0.30a), respectively. The dotted white hexagon indicates the boundaries of the central region. (b) The band structures calculated by the 2D plane-wave expansion method. X-axis indicates wavevector. The solid lines and the dashed lines correspond to a band structure of air hole radius 0.35a and 0.30a. The regions above the light line are filled by dark gray, in which modes are leaky. The transparent gray region indicates the photonic bandgap of a band structure with a radius of 0.30a. The circle corresponds to the first K point of the band structure with larger air holes, which is the operating point of our PBG-BE laser.

(a) Typical mode pattern images of PBG-BE lasers taken by an infrared camera. The dotted white hexagon represents the boundaries of the photonic bandedge mode region, which is same with the central region (I) of the SEM image. (b) Fourier space field pattern of the PBG-BE mode. (c) Top-view and (d) side-view of the calculated electric-field intensity profile of the PBG-BE mode. The dotted white hexagon indicates the boundary of the bandedge mode region. (e) side-view of the first K point bandedge mode operating at the finite PC pattern with no surrounding air hole. The intensity is indicated by a logarithm scale.

The normalized frequency of the PBG-BE laser as a function of air-hole radius (r/a) for each lattice constant, a, 325 nm 345 nm, 365nm, 390 nm, 414 nm, which are indicated by black, red, green blue, and cyan, respectively. The dots and the solid lines represent the measured lasing positions and the calculated ones by the 3D FDTD method. The inset is the measured polarization states of the laser.

Collected output power at the lasing wavelength is plotted for peak pump power. The threshold incident pump power is ~0.24 mW. The inset is the spectrum of the laser at the pumping power ~0.22mW. (b) The spectrum of the PBG-BE lasing mode at peak pump power of 0.35 mW.